Patent GB-1449983-A (GB)
Title: Flash welding
IPC: B23K11/24
Filed: 1974-07-16
Abstract: 1449983 Welding by pressure WEAN UNITED Inc 16 July 1974 [2 Aug 1973] 31474/74 Heading B3R [Also in Division G3] In a flash welding apparatus, when welding together two metal workpiece sheets of different thickness, control means operate to automatically align the horizontal centre lines of the two horizontally held sheets as shown Fig. 4. As shown Fig. 1, one sheet 21 is to be gripped between copper and steel inserts of a clamp 18, 23 the lower part 23 of which is fixed relative to the welding machine base 10<SP>1</SP>, on a horizontally slidable housing 15. The clamp upper part 18 is fixed to a slide 17 for vertical movement relative to the housing 15. A linear transducer LP1 e.g. potentiometer or a differential transformer senses the clamp gap. The other workpiece sheet 40 is to be gripped by a clamp 37, 42 the part 42 of which is fixed to a sub-base 31. The clamp part 37 is fixed to a vertical slide 36 supported by a housing 30 which is supported by side bars (not shown) of the base 10, for vertical movement. Eccentric drums 32 are journalled in sub-base 31 and have stub shafts (not shown) journalled in side bars of base 10. To vertically move the sub-base and hence the clamp portion 42, an electro-hydraulic cylinder 35 is coupled via a rod 34 to arms 33 rigidly fixed to the drums. A linear transducer, e.g. potentiometer LP2 senses the clamp gap. A further linear transducer, e.g. potentiometer senses the vertical distance between predetermined points on the base 10 and sub-base 31, and hence the vertical distance between the upper surfaces of the inserts in the lower portions 23, 42 of the clamps. Control circuit, Fig. 2.-Any difference between the clamps gaps due to unequal workpiece thickness when clamped, results in an output from a buffer amplifier OP3, the magnitude of which is proportional to the difference and the polarity of which indicates which gap is the greater. A unity gain amplifier OP4 produces an output proportional to half the gap difference (since the vertical correction required is half the difference in thickness of the sheets) and which is fed to the non-inverting input of OP5 via R5 for comparison with an output signal from OP6. Initially the cylinder 35 is manually operated to move the upper surfaces of the inserts of the two lower clamp portions 23, 42 into the same horizontal plane and a potentiometer P4 is adjusted to give zero output from OP6 when the said upper surfaces are so positioned. At the same time pot LP3 is manually adjusted so that it is near the centre of its travel, when its output voltage will be positive or negative voltage of from zero to less than the maximum applied voltage. Since the output voltage of pot LP1 is the greater, a positive voltage will be applied by OP4 to OP5 producing a positive output therefrom to energize a relay 2CR via a diode D2. The relay contacts will close causing the vertical motion means VMM (cylinder 35) to move the clamp 37, 42 and hence sheet 40 upwards. The output from LP3 therefore becomes more negative and the output of OP6 more positive. When the arithmetical value of OP6 output equals that of OP4, the output of OP5 drops to zero de-energizing relay 2CR to stop the vertical motion. The horizontal centre-lines of the sheet should now be in the same horizontal plane. Likewise, a relay 1CR is energized when the output of OP4 is negative, to move clamp 37, 42 downwards. Relay contacts 3CR prevent operation of relays 1CR, 2CR until the sheets are securely clamped. The pots LP1 to LP3 are shown on the nearside of the clamps. An identical set of pots and control circuitry are provided for the far side of the clamps (not shown).